I will discuss my activities as a postdoctoral fellow in the memory and probe technologies group at IBM Research. First, I will describe my work toward achieving high speed writing for probe-based data storage in polymers (the "Millipede" concept). In addition, I studied the pressure dependence of friction between silicon probe tips and polymer surfaces. The pressure-dependent component of the shear stress helps reduce the activation energy for atom-by-atom removal of tip material. Another aspect of my work is the discovery of a new surface interrogation method that employs thermoelectric cantilevers for off-contact thermal imaging. The integrated heaters in these cantilevers provide a useful alternative to other imaging methods for handling challenging topographies, limiting tip wear in high speed applications, and enabling combined imaging and manipulation schemes. Finally, I will briefly summarize my current investigations using conductive probes to characterize chalcogenide phase change materials for emerging memory devices.

Cyrus F. HirjibehedinLecturer/The London Center for Nanotechnology, University College of London

Monday, December 22, 2008, 10:30AM, Rm. H107, Bldg. 217

The spectroscopic capabilities of a scanning tunneling microscope (STM) can be used to measure the low energy excitation spectrum of individual nanostructures on surfaces with atomic-scale detail. Originally used to probe the vibrations of single molecules, inelastic electron tunneling spectroscopy can also measure magnetic excitations. We discuss recent studies in which we have used STM- based spin-excitation spectroscopy to determine the orientation and strength of the anisotropies for individual atomic spins on a copper nitride surface, as well as the interplay between magnetic anisotropy and Kondo screening. In structures containing more than one magnetic atom, we observe excitations of the coupled spin system that can change both the total spin and its orientation. We are able to describe the mechanisms that drive these inelastic spin excitations using a simple exchange coupling between the tunneling electron and the electrons that comprise the atomic spin. This description predicts the existence of a sum rule that includes a previously unnoticed type of spin-dependent elastic scattering, and evidence of both are seen in the observed spectra. We discuss the key factors that determine the relative strength of the inelastic tunneling, providing insight on when such processes can be observed and potentially how they might be enhanced.

Thin-film colossal magnetoresistance manganites such as La0.67Ca0.33MnO3 (LCMO) have now been intensely studied for more than a decade, but the issue of possible nanoscale electronic phase separation remains unresolved. Scanning Tunneling Microscopy / Spectroscopy (STS) has been pivotal in studying phase separation, but is hindered by being surface- rather than bulk-sensitive. For our sputtered LCMO films the data indicates a strong correlation between surface morphology and phase separation; rough films are phase separated while atomically flat films are homogeneous but have a more or less inactive surface layer. Regardless of surface morphology, the film-bulk is electronically and magnetically active. Many of the reported conclusions about electronic inhomogeneities measured by STS have been confused by this issue.

Erbium (Er) photoemission at the telecommunication wavelengths is found to be enhanced markedly by energy transfer from silicon nanocrystals (nc-Si) placed in close proximity of Er atoms. It is thus of great interest to fully understand the photoemission mechanism of nc-Si sensitized Er atoms and develop an optimal fabrication process and sample structures that would maximize the optical gain. Of particular interest is stratified multilayer film consisting of alternating polycrystalline Si and Er-doped Si oxide/nitride layers because of its simple fabrication process. Three related topics will be discussed for this endeavor. First, the dielectric constant of Si nanodots and nanoslabs was predicted to decrease as their size decreases, which was verified by variable angle spectroscopic ellipsometry, agreeing very well with the surface polarization effect theory. Second, simulations for multilayer films showed a large form birefringence and as much as 87% of power confinement in the low-index oxide layers for TM polarized Er light. The simulations were experimentally verified by prism coupler technique. Third, a lateral electrical injection scheme in multilayer films was devised and its preliminary results will be discussed.

While single-walled carbon nanotubes (SWNTs) have shown tremendous potential for electronic and energy applications, a comprehensive understanding of their electronic structure is still lacking. One crucial limitation has been the availability of broadband optical data on structurally characterized SWNTs, due in large part to the specificity of experimental techniques to a limited spectral range and subset of diameters as well as the inaccessibility of the lowest energy optical transitions (spanning the near and mid infrared) in large diameter semiconducting SWNTs. In order to address this challenge, we have developed rapid, broadband, and high-resolution spectroscopic techniques for studying both the visible and infrared electronic states on an individual SWNT. We have accomplished this using a process which combines observation of resonant enhancement in the spectra of elastic scattered supercontinuum laser light with an infrared Fourier transform photoconductivity methodology. We present our determination of the optical response over the range of 0.3 to 2.7 eV from a set of SWNTs and examine the scaling of the optical features as a function of diameter and subband index. In contrast to traditional bulk inorganic materials, we find that optical excitation in these 1D nanostructures results in moderately bound excitons under ambient conditions. As a result, the ultimate utility of these materials in energy applications, either directly or as composite materials, depends on the rapid and efficient dissociation of the excitonic state. Using results from our infrared photoconductivity measurement, we will discuss the challenges in determining the mechanisms and potential efficiencies for exciton dissociation and collection in these and other 1D materials.

TITANIA NANOFIBERS AS OXYGEN SENSORS

Daniela Dumitriu-LaGrangeUniversity of California

Monday, November 24, 2008, 10:30AM, Rm. H107, Bldg. 217

Transition metal oxides are widely used as catalysts in oxidation reactions and possess properties which are amicable for gas sensing. Among these materials, titania is attractive for gas sensing applications due to its n-semiconducting electrical character at moderate temperatures. Gas species interact with titania surface through charge transfer that can be monitored by changes in electrical conductivity. An improved surface reactivity and an increased concentration of electronic defects occur in nanostructured titanium oxides. Nanofibers arrangements prepared by annealing titania nanotubes have shown enhanced oxygen sensing capablities, e.g., their high electrical response is about two orders of magnitude higher than the values reported for coarse grained titanium dioxide. In addition to high oxygen sensitivity, these materials also have an extraordinarily fast (few ms) response time. The improved oxygen sensitivity of titania nanofibers is believed to arise from their enhanced electrical conductance controlled by surface defects states. Subsurface Ti interstitials and oxygen vacancies result from the surface dehydroxylation of titania nanotubes upon annealing. This seminar will discuss how titania structures with enhanced surface-to-bulk ratio, such as nanotubes and nanofibers arrangements, can be used for oxygen sensing devices with optimized characteristics (high sensitivity, short response time).

For further information contact James Liddle, 301-975-6050, James.Liddle@nist.gov

We have used a home built, low temperature magnetic force microscope (MFM) to image and to manipulate individual vortices in two classes of YBCO samples: a 200nm thick, optimally doped film; and detwinned single crystals, dozens of microns thick. In the film, if the force exerted by the magnetic tip of the MFM is strong enough to overcome the pinning potential, a pinned vortex jumps as a whole to a new pinning site. The behavior in the single crystals depends on the doping. For a slightly overdoped sample vortices stretch rather than jump when we drag them. The dragging distance in these crystals is anisotropic: it is easier to drag vortices along the Cu-O chains than across them, consistent with the tilt modulus and the pinning potential being weaker along the chains. We also find that when we wiggle the top of a vortex we can drag it significantly further than when we do not, giving rise to a striking dynamic anisotropy between the raster and the slow directions in a scan. In an underdoped single crystal, a material where superconductivity is so anisotropic that a vortex should be viewed as a stack of two dimensional pancakes, we show that vortices kink rather than tilt when we pull on them. These results demonstrate the power afforded by direct single-vortex manipulation and imaging for exploring the interesting behavior of these extended objects. Time permitting, I will discuss preliminary results on one of the new Pnictides, (Ba,K)Fe2As2, and on measuring contact potential variations during an MFM scan.

ELECTRONIC STRUCTURE AND TRANSPORT OF DISORDERED GRAPHENE

Enrico RossiCondensed Matter Theory Center, University of Maryland

Friday, November 14, 2008, 2:00PM, Rm. B165, Bldg. 220.

The unusual transport properties of graphene arise mostly from its Dirac spectrum. Close to the Dirac point the average carrier density vanishes and the density fluctuations are expected to dominate the physics of graphene. In this talk I will present a Thomas-Fermi-Dirac (TFD) theory to calculate the carrier density of graphene in presence of disorder. The approach is independent of the disorder source. I will present the results for the case when random charged impurities are the main source of disorder, the relevant situation for current experiments on exfoliated graphene. The TFD approach is able to quantitatively characterize the graphene density fluctuations at, and away from, the Dirac point, in good agreement with recent imaging experiments. In the second part of the talk I will discuss a transport theory for graphene, graphene Effective Medium Theory, that properly takes into account the strong density fluctuations close to the Dirac point and is able to answer semi-quantitatively some of the most puzzling questions that have been posed by transport experiments on graphene since its experimental realization.

Three-dimensional (3D) periodic micro- and nano-structures are of interest to a variety of fields, including microfluidics, tissue engineering, and photonic crystals. This has fueled the development of various 3D microfabrication techniques. Two especially promising approaches are colloidal self-assembly and interference-based lithography. In this talk I will focus on my work in both of these areas, and address their relevance to photonic crystals research.

First, I will discuss charge stabilized colloidal sediments. In these systems, strong electrostatic interactions give rise to colloidal crystals with long range order and large inter-particle separations. While they are highly ordered, these crystals lack the inter-particle contacts that impart mechanical stability, and thus do not retain their order when dried. In this work, the gradual addition of salt is used to attenuate the electrostatic repulsion. This contracts the colloidal lattice so that mechanically stable surface contacts are made. Using fluorescence confocal microscopy the particles' 3D locations are determined and their time resolved behavior is observed. This data is used to calculate translational and orientational order parameters that monitor changes in the crystalline structure.

Finally, I will describe the design and fabrication of 3D structures using interference lithography. In this approach, the optical interference generated by four or more coherent beams of light creates a 3D periodic intensity distribution that readily transfers into photoresist. The central issue I will address is how to design optics such that a desired 3D structure is produced. To this end, an approach using genetic algorithms (GAs) was developed and applied to the techniques of holographic and phase mask lithography (PML). Examples of GA-based designs that generate diamond-like photonic crystals will be presented along with recent progress using PML to experimentally demonstrate chiral microstructures.

For further information contact James Liddle, 301-975-6050, james.liddle@nist.gov

CNST Nanofabrication Research Group

TIME-RESOLVED PHOTOLUMINESCENCE AS A SENSITIVE PROBE OF CHARGE SEPARATION IN COLLOIDAL SEMICONDUCTING NANOCRYSTALS

Marcus JonesUniversity of Toronto, Department of Chemistry

Monday, November 10, 2008, 10:30AM, Rm. H107, Bldg. 217.

Electronic properties of nanomaterials such as colloidal CdSe nanocrystals (NCs) can be tailored by modifying their size and shape. This adaptability coupled with their ease of processability makes them very attractive materials for light-harvesting applications. Unfortunately the potential of NCs in photovoltaics have yet to be realized. This is due, in large part, to the complex electronic interactions of NC excitons with interfacial states and the surrounding environment, which can induce charge carrier dissociation into long-lived surface trap sites or external acceptor species. Unraveling the nature of these processes is a necessary step towards the creation of efficient NC-based solar cells, but progress in this field is significantly complicated by the inhomogeneous nature of NCs and by the involvement of states that are usually optically inactive. Time-resolved photoluminescence (PL) from CdSe nanocrystalline quantum dots reflects the radiative recombination rates from intrinsic exciton states and also contains information about non-radiative charge separation and recombination processes; however, interpretation of fluorescence transients is non-trivial and typical multi- or stretched exponential analyses yield little specific photophysical information. To address this problem, we have recently developed a method, based on classical Marcus electron transfer theory, whereby ensemble CdSe PL decays, measured over a wide temperature range, may be used to access pertinent information about the nature of charge separation processes in NCs. Using this method we are able to assess the influence of traps on the exciton population dynamics and, for the first time, quantitatively describe the transient PL of CdSe NCs in terms of well defined physical processes. These ideas can be extended to more complicated systems and I will discuss the potential for new PL-based techniques to probe carrier separation and recombination dynamics in multicomponent assemblies of NCs with molecules or other nanoscale systems.

PATTERN FORMATION OUTSIDE OF THERMODYNAMIC EQUILIBRIUM

Jorge Vinals, ProfessorMcGill University, Montreal, Canada

Monday, October 27, 2008, 10:30AM, Rm. H107, Bldg. 217.

Supramolecular chemistry offers promising routes for bottom-up fabrication of monodisperse, functional nanostructures. However, most applications require these nanostructures to be spatially ordered or aligned over macroscopic scales. Toward this end, we looked at methods of patterning and imposing spatial confinement on the micrometer and nanometer scales as ways to affect order in selected self-assembling systems, including DNS "origami" structures. 1-D peptide amphiphile (PA) nanofibers, and non-centrosymmetric mushroom-shaped supramolecular aggregates. In the first system, we were able to control the placement and orientation of DNA structures on chemically and topographically patterned surfaces and further use them to direct the assembly of nanoparticles. In the second system, PA nanofibers are patterned and aligned by soft lithographic techniques. We can guide the nanofibers around turns and show preliminary evidence that aligned nanofibers can direct cell behavior. Lastly, we use IR spectroscopy to probe the effect of surface chemistry and inclusion of a small molecule guest on the degree of order in thin films of polar, mushroom-shaped assemblies of rod-coli molecules.

For further information contact James Liddle, 301-975-6050, James.Liddle@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

EFFECTS OF PATTERNING AND SPATIAL CONFINEMENT ON ORDER IN SELF-ASSEMBLING SYSTEMS

Albert HundIBM Almaden Research Center

Thursday, November 6, 2008, 10:30AM, Rm. H107, Bldg. 217

The evolution of systems driven outside of thermodynamics equilibrium is characterized by strong nonlinearity and the formation of complex spatio-temporal patterns. We will give an overview of recent theoretical developments in this field, of the mathematical tools used in the description of these phenomena at the mesoscale, and of several applications in condensed matter physics, fluid mechanics, and materials science. In particular, we will describe recent research on self-assembly and defect motion in mesophases, with applications to microphase separation in block copolymers.

For further information contact James Liddle, 301-975-6050, James.Liddle@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

NON-LOCAL DETECTION OF PURE SPIN CURRENTS

Most spin-transport measurements have been performed in quasi-one-dimensional structures, where charge and spin transport is by default parallel. Recently there has been increased interest in investigating two-dimensional spin-transport structures, where charge and spin currents can be separated. This enables a direct determination of fundamental parameters for spin-transport, such as spin diffusion lengths, polarizations of injected currents, and spin Hall angles. First, I will discuss our work on lateral spin valves, where the pure spin currents are generated via electrical injection from a ferromagnetic contact (permalloy or cobalt) into a nominally non-magnetic metal (gold or copper). The measurement geometry is such that the charge current is drained at one end of the wire, while the spin diffusion is detected toward the opposite end. In this way a pure spin accumulation without a charge current is measured at the detection contact, which results in a large voltage contrast upon switching the magnetization of either the injector or detector. Using this technique we determined the spin diffusion length at 10 K to be 63?15nm for gold [1.2] and 200?20nm for copper [2.3]. Second, I will discuss measurements in mesoscopic gold Hall bars, where the pure spin current generation and detection is achieved via the direct and inverse spin Hall effect, respectively. These measurements confirmed the spin diffusion length for gold to be 64?2 nm and we also determined a giant value for the spin Hall angle ? = 0.11?0.03. --This work was supported by U.S. DOE Office of Basic Energy Science -- Materials Science under Contract No. DE-AC02-06CH11357.Ref: [1] Y.Ji, A. Hoffmann, J.S. Jiang, and S. D. bader, Appl. Phys. Lett.85, 6218 (2004). [2] Y. Ji, A. Hoffmann, J. S. Jiang, J. E. Pearson, and S. D. Bader, J. Phys. D: Appl. Phys.40, 1280 (2007). [3] Y. Ji, A. Hoffmann, J. E. Pearson, and S. D. Bader, Appl. Phys Lett.88, 052509 (2006).

Heat flow in materials usually follows ordinary perturbative wave theory, meaning it behaves in a linear fashion and dissipates uniformly. However, nonlinearity can cause directional heat flow, potentially leading to thermal rectification or the ability to control heat. Here we will discuss how nonlinear atomic vibrational modes occur in bulk and nanomaterials, their fundamental physics, and how they can be utilized to atomically control heat flow, leading to new energy-efficient technologies. Beyond heat flow, nonlinear modes also influence phase transformations, mechanical response, and crystal structure, which will be discussed.

IN-SITU STUDIES OF NANOSCALE PHENOMENA: ARE THE CHALLENGES WORTH TAKING?

Aman HaquePennsylvania State University

Monday, October 20, 2008, 10:30AM, Rm. H107, Bldg. 217.

High-resolution microscopy is more of a necessity than luxury in investigating nanoscale materials. In this talk, we elucidate this by discussing in-situ SEM/TEM (scanning/transmission electron microscopy) testing of mechanical behavior of materials. This approach provides unprecedented experimental capabilities such as simultaneously quantitative (strain-strain) and qualitative (deformation, dislocation, crack visulization) materials characterization, with the added benefit of monitoring 'cleanliness' of the experiments. Unfortunately, these environments (for examble, the TEM) have serous space restrictions and pose challenges with equal proportion because of the drastic miniturization required for the lab-on-a-chip type capabilities. We address the challenges using nanofabrication techniques and discuss several examples of micro/nanotechnology enabled experimental setups.While the focus of this talk remains on mechanical testing of nanoscale thin films or one dimensional materials, we present some new directions for the research in nanoscale materials for pressing applications such as energy conversion, sensors and actuators and micro-electronic devices. Particularly, we visit the multi-domain (thermal, electrical, mechanical etc) coupling phenomena, which can be predicted to be stronger than what we observe at the macro or even micro scales. An ongoing research on experimental multi-physics lab-on-a-chip will be presented.

ELECTRON DIFFRACTION AND INTERFEROMETRY WITH NANO-GRATINGS

Benjamin J. McMorranPh.D. Candidate, University of Arizona

Thursday, October 16, 2008, 10:30AM, Rm. H107, Bldg. 217.

We used nano-manufactured gratings to diffract and interfere low energy (0.3-5keV) electron matter waves. This demonstrates that nanostructures can be used for coherent electron optics, despite the keen sensitivity of low energy electorons to weak electromagnetic interactions. We use this sensitivity to probe the self-induced 'image charge' potential between moving electrons and the surfaces of the grating, which are less than 25nm away. We have observed several interference phenomena using electron beams with very different spatial coherence properties, and we have developed a theoretical framework based on Gaussian Schell-model beams that can efficiently model all types of interferometers that use diffraction gratings and partially coherent beams. I will discuss these experiments, their simulations, and the custom microscope we build for the research. I will also present ideas for future research directions afforded by electron interferometry.

For further information contact John Unguris, 301-975-3712, John.Unguris@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

OPTICAL NUCLEAR PHYSICS STEP 1: TRAPPING TH3+

Adam SteelePh.D. Candidate, Georgia Institute of Technology

Tuesday, October 14, 2008, 1:30PM, Rm. H107, Bldg. 217.

The nucleus of the 229-Th isotope is unique in that it possesses a very low energy (7.5 eV) nuclear isomer. It may be possible to someday drive this transition coherently, opening the way for a new kind of optical clocks and more precise measurements of fundamental constants. The Th3+ ion is an ideal candidate for such work because of its simplified level structure and potentially long trap lifetime. I will present the recent progress towards the realization of an optical nuclear frequencey standard, namely the trapping and observation of 232-Th3+ ions, by the Chapman and Kuzmich research groups at Georgia Tech.

NANOPARTICLES WITH KEY-LOCK INTERACTIONS: FROM SELF-ASSEMBLY TO DRUG DELIVERY

Alexei TkachenkoUniversity of Michigan

Thursday, October 9, 2008, 10:30AM Rm. H107 Bldg. 217.

Be decorating colloidal particles and other nano-objects with various biomolecules, one can introduce highly selective key-lock interactions between them. This leads to a new class of systems and problems in soft condensed matter physics. In my talk, I will review a number of theoretical possibilities and recent experimental achievements in this new field. First, I will discuss DNA-mediated self-assembly of nanostructures and nanoclusters. The specificity and tunability of the interactions result in a remarkable morphological diversity of in such systems. In some of the proposed schemes, DNA can be used to essentially "program" the self-assembly of a desired structure. The colloids with type-dependent interactions can also be used for experimental realization of one of the simplest self-replicating system. Its study may shed some light onto such important problems as prebiotic evolution and origin of life. Finally, I will discuss how cooperative key-lock binding can be also utilized to dramatically enhance cell specificity of drug delivery, e.g. in cancer treatment.

For further information contact James Liddle, 301-975-6050, James.Liddle@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

MEASURING AND CHARACTERIZING THE CONDUCTANCE OF A SINGLE MOLECULE

Joshua HihathArizona State University

Wednesday, October 8, 2008, 1:30PM, Rm. H107, Bldg. 217.

Measuring the conductance of a single molecule junction is becoming a standard measurement process in nanotechnology; however, there is a clear need for additional methods for measuring and characterizing a single molecule bound to two electrodes. This talk will discuss measuring the conductance of biological samples such as DNA and amino acids, as well as the development of new instruments for measuring and characterizing a single molecule junction. DNA studies were carried out in aqueous solution using readily available characterization techniques such as systematically changing the length, sequence, base-pair matching, temperature, and electrochemical potential of the system to attempt to elucidate the conduction mechanism. Such studies reinforced the need for faster measurement tools and better characterization techniques for single molecule junctions. Thus, the Conductance Screening Tool was developed to provide an order of magnitude increasing in the speed of measurement over previous designs. This tool has since been used to determine the conductance of individual amino acid residues without chemical modification. And finally, to advance characterization capabilities, a low temperature STM was developed and used to perform Inelastic Electron Tunneling Spectroscopy (IETS) on a single molecule bound to two electrodes. These measurements demonstrate that changes in the IET spectrum of a single molecule occur simultaneously with changes in the conductance and configuration of the molecular junction.

DISRUPTIVE TECHNOLOGIES THROUGH NANOSTRUCTURES

Fred SharifiGE Research

Monday, October 6, 2008, 10:30AM, Rm. H107, Bldg. 217.

As nanostructure technology continues to mature, fabrication processes which are compatible with realistic manufacturing techniques are now being developed. Consequently, disruptive technologies that were previously confined to laboratory test-beds are being implemented in commercial settings. This talk will focus on the impact of nanostructures in two areas: energy recovery and power electronics. Specifically, significant challenges associated with measurements and establishing of metrics for non-equilibrium charge and phonon transport in reduced-dimensional systems will be discussed.

CREATING HIGH PHASE-SPACE-DENSITY GAS OF HETERONUCLEAR MOLECULES

Josh ZirbelPh.D. Candidate, University of Colorado at Boulder

Monday, September 29, 2008, 10:30AM, Rm. H107, Bldg. 217.

I will present experiments creating heteronuclear diatomic molecules from ultracold, quantum degenerate mixtures of atomic bosons and fermions. The work presented takes advantage of a two-body scattering resonance, known as Feshbach resonance, to efficiently and selectively create the fermionic molecules. I will present studies of the weakly bound, highly vibrationally excited molecules created near the Feshbach resonance. These molecules participate in inelastic collisions with excess atoms in the trap. The inelastic loss rates are affected by the particular atoms involved in the collisions and are enhanced or suppressed depending on whether the colliding atoms are bosonic, fermionic, or distinguishable when compared to the molecule's consistuent atoms. I will also present recent work that has pioneered the making of high phase-space-density gases of ultracold polar molecules in the ro-vibrational ground-state.

STATISTICAL LIMITATIONS OF "TOP-DOWN" AND "BOTTOM-UP" NANOFABRICATION

Gregg GallatinApplied Math Solutions, LLC

Friday, September 26, 2008, 1:30PM, Rm. H107, Bldg. 217.

Historically, errors in lithography (the "top-down" approach) were dominated by engineering issues such as aberrations, bandwith, signal/noise, etc. But now lithography works at the nano-scale and fundamental physical principles have, in certain cases, become major sources of error. In contrast, self-assembly (the "bottom-up" approach) by it's very nature has always had to deal with fundamental statistical error sources such as, entropy, temperature, activation energy, etc.. Since both the "top-down" and "bottom-up" approaches will be used for nanofabrication in the future it is worthwhile to examine and compare the fundamental statistical limitations inherent in each approach. The "top-down" statistical issues that will be considered in this talk are how Quantum Mechanics limits resist edge smoothness, i.e., implies LER (Line Edge Roughness) and how Maxwell restricts illumination uniformity. With respect to "bottom-up", although the principles of statistical mechanics are well known there is still much that is not known about error generation in specific cases. To make a direct comparison with "top-down" in at least one particular case I will consider the edge variation statistics ("LER") of block-copolymers patterned using grapho-epitaxy.

For further information contact James Liddle, 301-975-6050, James.Liddle@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

ULTRACOLD PLASMA DYNAMICS IN A MAGNETIC FIELD

Xianli ZhangPh.D. Candidate, University of Maryland

Wednesday, September 24, 2008, 1:30PM, Rm. H107, Bldg. 217.

Ultracold plasmas created by photoionizing a sample of laser cooled and trapped cold atoms, has extended the neutral plasma parameters by about two orders of magnitude, as the electron temperatures as low as 1 Kelvin. Previous studies focused on the study of free expansion and electron temperature measurement of the plasma without a magnetic field. In this talk, I will talk about a new technique, time-of-flight projection imaging technique, to study ultracold plasma dynamics with or without a magnetic field, such as plasma expansion and instabilities.

TOWARDS QUANTUM INFORMATION PROCESSING USING SINGLE NEUTRAL ATOMS

To realize quantum information processing with neutral atoms, controlled coherent interaction between them is a fundamental requirement. One approach relies on deterministic coupling of two or more atoms to the mode of a high-finesse optical resonator in the strong coupling regime. We investigate such a coupling between neutral atoms and a resonator under controlled conditions: we load a chosen number of Doppler-cooled caesium atoms from a magneto-optical trap into a standing wave optical dipole trap. The positions of the individual atoms are then determined with sub-micrometer precision, enabling us to prepare, to manipulate and to read out the quantum state of each atom. Using the dipole trap as an optical conveyor belt, the atoms are transported into the mode of a high-finesse optical cavity with a finesse of F=106, leading to a maximum single-atom cooperativity parameter of the order of 50.By observing the transmission of a weak resonant probe laser we can detect the interaction dynamics of a single atom coupled strongly to the cavity field. Cooling by the probe laser extends the observation time to several ten seconds, allowing us to investigate the strength and the stability of coupling, which are crucial parameters for the controlled coherent interaction. Moreover, we analyze the atom-field interaction using a method, essential for the creation and measurement of entanglement.

In the recent years, nano-refrigeration using electron tunneling in hybrid Normal metal - Insulator - Superconductor (N-I-S) junctions has gained increasing attention [1]. Its basic principle is the energy selective tunneling due to the presence of an energy gap in the superconductor density of states. With a sub-gap voltage bias, only the most energetic electrons can tunnel out of the normal metal, leaving behind the electrons with less energy.We have measured with a high resolution the differential conductance of S-I-N-I-S junctions, whose analysis gives us an access to the normal metal electronic temperature as a function of the voltage. A quantitative model is proposed, that includes the electron-phonon coupling and the Kapitza resistance at the interface with the substrate. With this model, we have achieved a thorough description of the charge and heat currents [2]. We have also shown that the normal metal phonon temperature drops significantly below the substrate temperature. At very low temperature (T 200mK) and low bias, the phase coherent Andreev current dominates the quasi-particle current. By analyzing quantitatively the heat balance in the S-I-N-I-S junction, we demonstrate that the Andreev current does carry heat. This thermal contribution heats the normal metal electrons, overriding over a large voltage range the tunneling-based cooling [3].

For further information contact James Liddle, 301-975-6050, james.liddle@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

COLD RYDBERG ATOMS

Photo-excitation of atoms in laser-cooled gases allows the creation of gases of cold Rydberg atoms. In these gases at higher densities, rich dynamics stem from electric multipole interactions among the Rydberg atoms. For example, interatomic forces between Rydberg atoms cause state-changing collisions which can significantly increase the kinetic energy of the colliding atoms. I will discuss experiments examining these collisions in which internal energy of the Rydberg atoms is converted into kinetic energy. At lower densities, translationally cold Rydberg atoms are well-suited for spectroscopic studies to measure atomic properties. I will present a recently proposed scheme for driving transitions between Rydberg states via a time-dependent ponderomotive interaction between the Rydberg electron and an applied optical field and discuss experimental efforts to realize this new spectroscopic tool.

THE NONLINEAR AND LINEAR PHENOMENA IN SILICON NANOSTRUCTURES

Jidong ZhangDept. of ECE, University of Rochester.

Tuesday, August 19, 2008, 10:30AM, Rm. H107, Bldg. 217.

Silicon photonics has attracted much attention recently because of its potential for providing a monolithically integrated platform for both linear and nonlinear applications. In this presentation, I'll talk about our recent result on the application of silicon photonics, in both linear and nonlinear regime, including the measurement of silicon's nonlinearities, the formation of optical solitons in a silicon waveguide and EO modulator based on silicon photonic crystal and novel EO polymer.

Nanostructures, including single molecules, carbon nanotubes and semiconductor nanowires often exhibit excellent characteristics that are comparable, and in some cases even superior, to the properties of traditional semiconductors. Their electrical and optical properties are determined by the complex interplay between multiple processes occurring in differing length and time scales. Exploring electrical and optical phenomena at this scale therefore requires a tool to investigate these complex, multi-scale processes at the system-wide level.In this talk, I will discuss our approach to investigate the coupling between electronic motion in 1D and 2D nanostructures (nanotubes, nanowires and single layer graphene) and various physical properties, including the electron band map, contact energy barriers, and electron phonon couplings. In particular, we recently developed a novel laser-based microscopy for addressing electrical conductance properties of a large number of individual nanostructures. We applied this technique to successfully characterize a large number of carbon nanotubes grown over a macroscopic area (~millimeters) with a high throughput ( 100/min). Our technique is an important step toward a real-time chemical imaging with which one can monitor electrical conductance change of an array of nanostructures while they are exposed to various chemical reactions.

For further information contact James Liddles, 301-975-6050, james.liddle@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

NANOSCALE MEASUREMENTS FOR PHOTOVOLTAICS: ADVANCES AND CHALLENGES

Aurelien PasquierResearch Assistant Professor, Rutgers University.

Tuesday, July 29, 2008, 10:30AM, Rm. H107, Bldg. 217.

The quest to control semiconductor morphologies at the nanoscale has been largely motivated by the prospect of obtaining interesting new properties differing from the bulk. In the case of photovoltaic applications, bandgap modification can be obtained from quantum confinement below the exciton Bohr radius in nanodots, and charge mobility can significantly increase in nanowires and nanorods, because of reduced grain boundaries. The discovery of new photovoltaic structures such as bulk organic heterojunctions and semiconductor nanowires has also created the need for new characterization methods than can probe the local structure at the scale of exciton diffusion length, and correlate it with overall device power conversion efficiency.Nanostructured semiconductors such as single wall carbon nanotube transparent conducting films, Zinc oxide nanotips arrays, and Germanium nanowires coatings have been developed at the Rutgers Institute for Advanced Materials, Devices and Nanotechnologies (IAMDN). We will present their evaluation in photovoltaic devices, and illustrate some of the challenges that such measurements represent. For instance, photoelectrical measurement of nanosized objects is made difficult by the need to make electrical contact to them. A preferred approach is to generate phase-locked photocurrent and photoluminescence with a nanosized spot of chopped light, and build an image by mapping the sample. We will report our initial results towards this goal with photocurrent microscopy on silicon solar cells, and discuss strategies to increase resolution from tens of microns to tens of nanometers. Finally, we expose our plans to measure local photoluminescence quenching and exciton lifetime in nanoscale photovoltaic objects.

The fabrication of nanometer-scale features such as quantum dots and quantum wires, in a controllable and economically viable manner is one of essential requirements for the production of highly functional devices. Here, we propose a new electron beam projection lithography technique for patterning nanometer scale, periodic structures. The novelty of this technique is that the crystalline lattice image observed by high resolution transmission electron microscopy (HRTEM) is employed as the ultimate mask to define nanometer scale pattern. Namely, the Ångstrom-scale lattice image of a crystalline material is magnified within the electron microscope, and is projected onto an electron-beam-resist-coated substrate. This technique is tentatively called AIPEL (Atomic Image Projection Electron-beam Lithography).To experimentally prove this concept, we developed the specially designed hardware based on the modification of a 200 kV TEM with a field emission gun (JEM-2010F, JEOL Ltd.). The patterning lenses for controlling the patterning magnification (50 to 300 times) were inserted below objective lens, and the wafer stage for loading the resist-coated wafer was installed in the lithography plane, as shown in Fig. 1. Using this technique, we successfully fabricated periodic arrays of dot and line patterns with feature sizes of about 25 nm using single-crystalline Si as the mask materials. Moreover, the HRTEM images which can be obtained from crystalline samples can be far more complicated. Fig. 2 shows the various patterned structures obtained from crystalline ?-silicon nitride (?-Si3N4) sample with hexagonal crystal system (P63/m). The patterning results of these complicated and interesting nanostructures not only demonstrate the uniqueness of this method but also open up a whole new area of investigating a variety of electrical, optical, and magnetic properties of nanostructures.

FOCUSED ION AND ELECTRON BEAM NANOFABRICATION: NEW DEVELOPMENTS

John MelngailisDept. of Electrical and Computer Engineering, University of Maryland.

Friday, July 25, 2008, 11:00AM, H107 Rm., 217 Bldg.

Both focused ion beams and electron beams can be used for direct, maskless, resistless nanofabrication as well as for lithography. So far the direct fabrication has been limited to applications such as photomask repair, circuit restructuring, failure analysis, and the creation of various highly specialized structures. Recent developments in maskless fabrication, so far aimed mainly at resist exposure, suggest that this picture might change. For example, IMS in Vienna, Austria is developing an instrument that can be characterized as an ion beam or electron beam dot matrix printer. The total current on the sample available from this kind of instrument is at least three orders of magnitude larger than from a single beam instrument. This may lead to new applications of charged particle beam fabrication, as well as enable applications considered in the past but rejected because of very low throughput. An example of one such application is the direct writing of the identity in RFID tags using ion beam implantation. Recently we have also shown that electron beams can be used to deposit relatively pure platinum from an inorganic precursor gas, Pt(PF3)4. Such metal deposits can be used as contacts to carbon nanotubes, semiconductor nano wires, organic fibers, or other structures where conventional lithography is impractical.

There have been many efforts in the past decades to improve the spatial resolution of transmission electron microscopes but little in way of improving the temporal resolution of in situ transmission electron microscopy. Most materials dynamics occur at rates much faster than can be captured with standard video rate acquisition methods. Thus, there is a need to increase temporal resolution in order to capture and understand salient features of these rapid materials processes. To meet the need for studying fast dynamics in material processes, we have constructed a nanosecond dynamic transmission electron microscope (DTEM) at Lawrence Livermore National Laboratory to improve the temporal resolution of in-situ TEM observations. The DTEM consists of a modified JEOL 2000FX transmission electron microscope that provides access for two pulsed laser beams. One laser drives the photocathode (which replaces the standard thermionic cathode) to produce the brief electron pulse. The other strikes the sample, initiating the process to be studied. A series of pump-probe experiments with varying time delays enable, for example, the reconstruction of the typical sequence of events occurring during the martensitic phase transformation. This presentation will discuss the core aspects of the DTEM instrument and how the DTEM has been used to study rapid solid-state phase transformations and chemical reactions. The latter half of the talk will layout near-term instrument development plans to extend the current 15ns-10nm spatio-temporal resolution and single frame acquisition to a versatile instrument that can explore material dynamics on the sub-picosecond to microsecond time scales and capture multi-frame movies of the transients states in material processes. Work was performed under the auspices of the U.S. Department of Energy, Lawrence Livermore National Laboratory and supported by the Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under contract No. DE-AC52-07NA27344.

For further information contact James Liddle, 301-975-6050, james.liddle@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

LOW ENERGY-SPREAD ION BEAMS FROM A TRAPPED ATOMIC GAS

Edgar J. D. VredenbregtDr./Department of Applied Physics, Eindhoven University of Technology. The Netherlands

Monday, July 21, 2008, 10:30AM, H107 Rm., 217 Bldg..

Pulsed and continuous ion beams are used in applications such as focused ion beams. The smallest achievable spot size in focused ion beam technology is limited by the monochromaticity of the ion source. Here we present energy spread measurements on a new source concept, the ultracold ion source [1,2]. It produces ion beams by near-threshold ionization of laser cooled atoms. In recent detailed particle tracking simulations we found that the brightness of such a source can compete with that of the industry standard liquid metal ion source (LMI) but offers the advantage of reduced longitudinal energy spread [1].In the experiment, rubidium atoms are captured in a magneto-optical trap inside an accelerator structure where they are ionized by a pulsed laser in a DC electric field. The resulting cold ion bunch is accelerated towards a multi-channel plate detector where the time-dependent ion current is measured. The relative spread in time of flight to the detector is a good measure for the relative longitudinal energy spread in the bunch. Two order of magnitude lower energy spread is achieved compared to the liquid-metal ion source. Bunches with an energy of only 2 eV are produced with an rms energy spread as low as 0:01 eV.

MAGNETIC MATERIALS: MORE THAN WHAT YOU SEE EVERYDAY

Electricity, sound, motors, information storage, sensors... Magnetic materials play an important role in these applications and are crucial for many aspects of modern life. Traditional applications of magnetic materials are based on the interaction between the magnetic materials and the electric fields generated by currents. Newer applications are based on the direct interaction between these materials and current. The 2007 Physics Nobel Prize for Giant Magnetoresistance is an example of this newer interaction. In this talk I describe the interactions between currents and magnetic fields and discuss some of the ways in which this interaction is exploited.

NOVEL APPLICATIONS OF CONTROL THEORY AND INFORMATION THEORY

Pramod MathaiGraduate Research Assistant/University of Maryland.

Friday, July 11, 2008, 10:30AM, Rm. A129, 216 Bldg.

Novel applications of Control theory and Information theory This talk will be focused on two novel applications of Controls and Information theory: A) A control-theoretic approach for creating accurate interconnections of reduced order models, and its application to modeling heat conduction in electronic devices. B) Using the concept of 'directed information' to identify network topologies and its application to inferring biological gene transcription networks.

COLLOIDAL NANODEVICES

Dr. David PeyradeColloidal Nanodevices Team.

Thursday, July 10, 2008, 1:30PM, Rm. H107, Bldg. 217.

I will propose alternative strategies developed in the ColloNa team to manipulate (assembly, localize, separate...) colloidal nanostructures and evaluate the asets of these methods in terms of nanoengineering, and nanomachining. I will show that the integration of colloidal nanostructures into nanodevices can be studied in real-time by Capillary-Force-Assembly (CFA): CFA is based on the control of capillary force to overcome colloidal Brownian motion at the triple contact-line during solvant dewetting accross a patterned surface. We study dynamically several strategies (bath, drop or microfluidic cell evaporation control) to assemble, or individually localize, inorganic colloidal nanostructures into predefined patterns. I will present a low-cost global strategy to collectively realize Single-Nanostructure Device. It is based on the combination of Nanoimprint lithography and colloidal dielectrophoresis trapping at the single particle level. Finally, I will detailed physical properties of colloidal/supra-colloidal nanostructure such as single Au-nanoparticle coulomb blockade or spectroscopic properties of deterministic gold colloidal assemblies.

ADVANCES IN STRUCTURAL FE-BASED MAGNETOSTRICTIVE ALLOYS

Alison FlatauDepartment of Aerospace Engineering, University of Maryland. College Park, MD

Monday, July 7, 2008, 2:00PM, H107 Rm., 217 Bldg..

Magnetostrictive materials belong to the family of smart materials that are enabling major advances in noise, vibration and shape control and new approaches to structural health monitoring. An introduction to magnetostrictive materials will be presented, followed by an emphasis on the new structural magnetostrictive alloy Galfenol with discussion of current and potential applications that range from nano-and mems sensors to large scale sonar devices. The presentation will include a summary of on-going research in our ONR MURI Program that in addition to the Univ. Maryland, includes researchers from Iowa State Univ., Univ. Minn, Ohio State, Penn State, Rutgers and Va Tech. This program is focused on structural magnetostrictive alloys, with an emphasis on the iron-gallium alloy known as Galfenol. A discussion of some of the challenges associated with transitioning this relatively new alloy to commercial scale production and thoughts on taking advantage of its unique structural attributes (e.g. ductility and a negative Poison's ratio) will be included in the presentation.

For further information contact John Unguris, 301-975-3712, john.unguris@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

IN SITU EXPLORING THE PROPERTIES OF NANOMATERIALS AND NANOSTRUCTURES INSIDE A TEM

Zhiwei ShanSenior Scientist.

Friday, June 27, 2008, 1:30PM, Rm. H107, Bldg. 217.

Studying the dynamic behavior of materials/device in response to external stimuli such as stress, temperature and electrical fields can provide important and novel understanding towards better applications. In situ TEM is a powerful tool for this purpose due to its high spatial & time resolution. Using in situ TEM tensile technique with dark field observation, for the first time, we provided compelling experimental evidence of grain boundary mediated plasticity in nanocrystalline Ni, which has been sought for many years (Shan et al, Science, 2004 and 2005; Shan et al, PRL, 2007 and 2008). More recently, we have developed a quantitative in situ TEM mechanical testing device with which, we can perform miniaturized compression tests inside a TEM and build one-to-one relationship between the mechanical data (force, displacement vs. time) and the microstructure when materials are subjected programmed deformation. In this talk, we will demonstrate that submicrometre nickel crystals with high density initial defects can be made dislocation free by applying purely mechanical stress. This phenomenon, termed 'mechanical annealing', leads to clear evidence of source-limited deformation where atypical hardening occurs through the progressive activation and exhaustion of dislocations sources (Shan et al, Nature Materials, 2008). Lastly, a discussion on in situ TEM techniques that hold great promise to improve our understanding of the origins of mechanical, thermal, electrical properties and of how these properties coupled will be presented.

For further information contact James Liddle, 301-975-6050, james.liddle@nist.gov

Oxides are of interest for fundamental studies and technological applications due to their wide range of electronics properties (metallic, insulating, superconducting) and polarizable behaviors (ferroelectric, ferromagnetic). In addition, the properties of oxides at surfaces and interfaces often differ from the bulk materials. For example, many of the oxides predicted to be half metals (i.e., 100% spin-polarization) show lower than expected magnetoresistances in magnetic tunnel junctions (MTJs). Also, ferroelectric oxides often have much higher dielectric losses in thin films versus bulk single crystals. Magnetism and transport in MTJs will be discussed as a way to probe the interface behavior in magnetic thin films. In particular, MTJs with electrodes of magnetite Fe3O4 and the colossal magnetoresistance material La0.7Sr0.3MnO3 (LSMO), which are magnetic materials predicted to be half metals, were studied with both magnetic and nonmagnetic insulating barrier layers in order to understand the effect of magnetic moments in the barrier. The junction behavior was examined as a function of barrier thickness, bias, and temperature in order to determine the conduction mechanisms at work in the junctions. In addition, the effects of strain on the microwave electronic properties of ferroelectric thin films were studied because these materials hold promise for microwave applications due to their high tunability of the dielectric constant and low loss at microwave frequencies. The dielectric properties of barium strontium titanate films were examined as a function of lattice structure distortion. X-ray absorption fine structure (XAFS) measurements were used to probe the local atomic structure of the films. These results helped in analyzing the microwave measurements and supported theoretical modeling of the film strain effects, which heavily depended on the direction of strain, the presence of strain-induced permanent polarization, and (if present) the direction of the permanent polarization with respect to the direction of the electric field.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

The evolution of Single-Photon Avalanche Diodes (SPAD) and associated electronics for photon counting and timing applications is quickly reviewed. The fabrication of monolithic SPAD Arrays in silicon technologies is discussed. The development of InGaAs/InP SPADs modules for the near-infrared is presented.

FABRICATION AND ELECTRICAL CHARACTERIZATION OF NOVEL DEVICES FOR LARGE-AREA ELECTRONICS

Behrang HamadaniSemiconductor Electronics Division, National Institute of Standards and Technology.

Monday, June 9, 2008, 10:30AM, Rm. H107, Bldg. 217.

Electronic materials such as polymeric or small-molecule organic semiconductors, transparent metal oxides, nanowires etc, and the optoelectronic devices based on these materials offer potential advantages such as low cost, large-area patterning and flexibility over their classical counterparts. Electronic displays incorporating organic light emitting diodes have already been commercialized and research efforts for integrating organic based transistors and solar cells in commercial applications are well under way. Realization of these efforts, however, requires advanced device characterization and optimization. Of particular interest is the fundamental physical understanding of the mechanism of charge transport at the semiconductor/insulator interface in organic thin film transistors and charge injection at the contacts to the semiconducting material.In this talk, I will present our findings on the effect of contact resistances on charge injection and transport within the channel of organic thin film transistors using a variety of measurement techniques, including temperature dependent current-voltage characterization and a novel capacitance-voltage analysis to gain fundamental insight into the electrical performance of these devices.

EXTREMUM-SEEKING CONTROL OF CAVITY FLOW WITH COMPENSATION OF ACTUATOR DYNAMICS

The flow over a shallow cavity produces self-sustained oscillations caused by coupling between flow dynamics and flow-induced acoustic field, leading to intense pressure fluctuations. Suppression of these pressure -- a configuration occurring in many practical applications, from landing gear wells to weapon bays -- has been a canonical problem for exploring active flow control technologies. For the development of active cavity flow control strategies, although feed-forward schemes have been attempted with various degrees of success, the most significant effort has been spent on feedback control in recent years. This talk presents a novel approach to the development of a feedback control system for suppressing the resonant tones emanating from the cavity. Firstly, a simple but effective linear feedback control law, which is derived based on a simplified Galerkin system, is employed. Secondly, an extremum-seeking algorithm is implemented to optimize in real time the control parameter in such a way that the magnitude of a limit cycle is minimized in closed-loop. Furthermore, a dynamic compensator is synthesized and integrated into the overall feedback system, in order to regulate undesirable actuator dynamics. From the experimental results, the proposed adaptive control demonstrates the superiority over fixed-structure control in terms of coping with varying flow conditions.

For further information contact James Liddle, 301-975-6050, james.liddle@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

THE PHYSICS OF SURFACE WAVES AT THE METAL-DIELECTRIC INTERFACE INTERACTING WITH STRUCTURES OF SUBWAVELENGTH SCALE

John WeinerProfessor.

Thursday, June 5, 2008, 10:30AM, Rm. H107, Bldg. 217.

The localization, enhanced transport, and transmission of light along and through subwavelength structures holds promise for chip-scale photonic circuit integration, biological sensors, and dense optical storage media. The basic physics of this transport and transmission has been, however, imperfectly understood and attempts to rationalize early experimental results from the perspectives of crystal periodicity, classical physical optics, diffraction, and classical electrodynamics have led to diverse and often conflicting interpretations and predictions. We present here a series of studies seeking to explain the fundamental physics of a single propagating mode interacting with a single subwavelength structure and how this physics relates to transport and transmission through periodic arrays of such structures.

TERAHERTZ OPTOELECTRONICS: NEW DEVICES, TECHNIQUES, AND APPLICATIONS

Amit K AgrawalUniversity of Utah. Salt Lake City, UT

Tuesday, June 3, 2008, 1:30PM, Rm. H107, Bldg. 217.

The terahertz (THz) spectral range has traditionally been referred to as the gap in the electromagnetic spectrum. While there has been recent success in developing sources and detectors, there has been little work in the developing device technologies. The use of plasmonics, which refers to surface excitations at metal-dielectric interfaces, is aggressively being pursued to develop the requisite capabilities. This approach offers several attractive features such as the possibility for a simplified device topology, subwavelength field localization, and low-loss transmission of THz radiation. I will describe my work in understanding the properties of surface plasmons at THz frequencies and its relevance to developing unique and useful THz optoelectronic devices.

Dr. Mark HoeferMagnetics Group, National Institute of Standards and Technology.

Friday, May 16, 2008, 1:30PM, Room H107, Building 217.

The recently discovered spin transfer effect enables the application of localized torques in magnetic thin film nanostructures. In the point contact geometry, this effect can result in large amplitude spin wave generation. The well studied Slonczewski model of spin torque in trilayer nanostructures is the Landau-Lifshitz equation modified with a local spin torque term. In this talk, a non-local model of point contacts in single layer thin magnetic films is presented and studied numerically in two spatial dimensions. Here, the spin torque term in the Landau-Lifshitz equation is non-local and is due to spin diffusion effects. A variety of quasi-periodic mode solutions to this equation are found including localized standing waves, vortex spiral waves, and a weakly diffracting collimated beam of spin waves, the direction of which can be steered by changing the direction of an applied magnetic field. The spin wave beam appears to be the nonlinear hybridization of the vortex spiral waves and the localized standing wave. Mode selection is explained using linear spin wave theory.

VIBRONIC VIRTUALIZATION IN MOLECULAR NANOSTRUCTURES

Gabriel ZeltzerApplied Physics Department Stanford University.

Friday, May 2, 2008, 11:00AM, Rm. H107, 217 Bldg.

Controlling matter at the spatial limit holds promise in both fundamental scientific research as well as applications in nanotechnology. Atomic and molecular manipulation on surfaces has opened a new realm of possibilities where materials can be engineered and artificial structures can be constructed with a bottom-up approach, one building block at a time. We study atomically precise nanostructures assembled from CO molecules on Cu(111). The control of electronic and vibronic states is demonstrated in several coherent quantum geometries. This work has revealed a "vibronic virtualization" process where non-local vibrons are synthesized and focused with a 2DEG surrounding molecular oscillators.We will briefly discuss the design and performance of the atom-manipulation apparatus that has enabled these experiments. We conclude with an outlook for the next step in this class of experiments, in which STM may be combined with quantum force sensing through the use of quartz tuning forks.

NONLOCAL AND LOCAL MAGNETIZATION DYNAMICS EXCITED BY A RF MAGNETIC FIELD IN MAGNETIC MULTILAYERS

Takahiro MoriyamaGraduate student, University of Delware.

Thursday, April 24, 2008, 10:30AM, Rm. H107, 217 Bldg.

A microwave study in spintronic devices has been actively pursued in the past several years due to its fertile physics and potential applications. A passive use of microwave can be very helpful to understand the spin dynamics in spintronic devices. On the other hand, an active use of microwave yields a great potential for interesting applications which gives new functionalities into spintronic devices. For instance, a spin wave excitation by a rf field can be used to reduce the switching field of a ferromagnet, which could be potential applications in an advanced recording media. More interestingly, a precessing magnetization driven by a rf field can inject spin currents into a neighboring layer, i.e. nonlocal magnetization dynamics (or spin pumping effect) which is one of the candidates for generating a pure spin current. In the talk, I will present my work on a microwave study in magnetic multilayers and magnetic tunnel junctions and show the experimental results of the local and non-local magnetization dynamics excited by a large rf magnetic field.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

Two dimensional nanomaterial arrays are important platform for many applications. Despite many efforts, organizing nanomaterials into desired structures is a grand challenge in nanoscience and technology. In this presentation, a polymer template approach for synthesizing uniform metal nanoparticle arrays with controlled particle size and interparticle spacing will be demonstrated. These metal particle arrays are ideal model catalysts for fuel cell research and are used to reveal the catalyst structure-activity relationship. O2 reduction as well as CO oxidation will be used as examples to illustrate the applications of the metal nanoparticle arrays in electrocatalysis. In addition to catalysis, these metal nanoparticle arrays can be used as the seed to form other organized nanomaterials. Results from the seed-mediated growth and electrochemical deposition will be discussed to demonstrate the applications of the metal nanoparticle arrays in material synthesis. Some measurement challenges in these applications will also be discussed.

CAVITY QED WITH CHARGED QUANTUM DOTS

Matthew RakherGraduate Student Researcher - UCSB Dept. of Physics.

Friday, April 18, 2008, 1:30PM, H107 Rm., 217 Bldg.

We report on nanodevices that for the first time allow for charge tuning of single InAs quantum dots located near the field maximum of high quality micropillar cavities. Through the innovation of a novel trench style cavity design, we are able to embed doped layers for electrical gating within a microcavity and obtain Q values greater than 50,000. Using these devices, we demonstrate record high single photon count rates with a capture efficiency of 38{\%} and a Purcell effect up to 8. We also show high frequency polarization modulation of single photons enabled by Stark shift tuning a charged quantum dot between two polarization modes of a slightly elliptical micropillar with frequencies up to 100 KHz. Furthermore, we demonstrate a charge tunable quantum dot coupled to a micropillar cavity mode, which is an important step in quantum communication protocols involving trapped single electrons or holes. This type of device enables a quick, non-destructive measurement of the spin state of the trapped charge.

POSSIBLE ORDERED STATES IN GRAPHENE BILAYERS

Hongki MinUniversity of Texas at Austin.

Friday, April 4, 2008, 1:30PM, Rm. H107, 217 Bldg.

Graphene is a two dimensional honeycomb lattice of carbon atoms which has recently attracted considerable attention because of rapid experimental progress, and because of its novel physical properties. In this talk, I will discuss recent theoretical work in which I have proposed new types of ordered electronic states in graphene bilayers, including excitonic superfluids which could have remarkably high transition temperatures. My talk will conclude with some speculations on the possibility of radically new types of electronic devices in these systems whose operation is based on collective electronic behavior.

ORTHOGONAL TRACKING MICROSCOPY

Matthew McMahonPhysicist NIST.

Thursday, April 3, 2008, 1:30PM, Rm. H107, 217 Bldg.

Discussion of recent work in 3D particle tracking using a new technique called Orthogonal Tracking Microscopy, with samples that were prepared in the Nanofab. Current efforts to fabricate anisotropic fluorescent polymer particles for tracking studies will also be discussed.The Nanofab Users Information Meetings provides an opportunity for users to present work and comments to the Nanofab staff. If you have an idea about a topic you would like to hear more about or if you are interested in presenting to the group please contact. Anthony Novembre at: anthony.novembre@nist.gov Ext. 2886

Folding nanopatterned membranes at arbitrary angles, like origami, allows one to manufacture 3D nanoscale systems. One challenge with this approach is to achieve very small fold radii for tight 3D packing. Stress induced on a thin membrane by helium ion implantation will fold the membrane to a one-micron radius. Incident ion energy and fluence determine the fold angle and direction, and are easily controllable. One application of stress folding is a chemical sensor. Built from a membrane as a 3D micro-switch, the stress that develops in a reactive polymer bends the switch closed. Thus, it consumes little power and responds to target gases with more than a million-fold electrical resistance change. Other 3D membrane architectures may require accurate feature-alignment. This is solved by patterning membranes with magnetic material so they attract in self-alignment when folded together. These advances open the way for future applications to optical devices, for example, artificial dielectrics such as photonic crystals and more general non-periodic metamaterials, which are formed by combining new optical exposure techniques with membrane folding.

VISION-BASED CONTROL VIA A LYAPUNOV-BASED APPROACH

Guoqiang HuPostdoctoral Research Associate - University of Florida.

Monday, March 24, 2008, 1:30PM, H107 Rm., 217 Bldg..

Recent advances in visual sensing hardware, image processing/interpretation technology, and computational capability generate a golden opportunity to do real-time vision-based feedback control. This talk will describe research work on vision-based control that is obtained by exploiting a combination of multi-image photogrammetry, homography techniques, a quaternion parameterization, and Lyapunov-based nonlinear and adaptive control methods. Multi-image photogrammetry will be described as it relates to developing a measurable translation and rotation error system (via a homography decomposition) in both Euclidean and quaternion representations. New visual servo tracking control results will be described for a camera system moving with unconstrained motion. The desired trajectory to be tracked is represented by a sequence of images (e.g., a video), which can be taken online or offline by a camera. This control scheme is singularity-free and can compensate for the unknown depth information in visual feedback while achieving the asymptotic tracking results. The proposed method has been verified in a hardware-in-the-loop experimental system for simulation and test of autonomous vehicles. Vision-based control methods motivated by some open issues will also be briefly presented.

In this talk, I will present the latest results from two research projects in CNST. In the first part, I will discuss new methods for bringing erbium atoms to ultracold temperatures by exploiting the unique laser-cooling properties of this strongly magnetic rare-earth element. The capability to cool, trap and manipulate erbium has applications for developing nanoscale optical devices and may provide access to new regimes in the study of magnetically interacting quantum gases. In the second part, I will discuss a recent breakthrough in tracking the motion of freely diffusing (solution-phase) particles using optical microscopy. A major stumbling block in achieving real-time control of individual molecules or nanoparticles is the difficulty of quickly and accurately extracting accurate position information from a CCD image. We recently developed a new computational method for extracting such information, capable of localizing particles to a few nanometers through a fast and flexible algorithm.

IMAGING OF SCREENED POTENTIAL AND SUPERCONDUCTIVITY IN NANOSCALE SPATIAL RESOLUTION BY LOW-TEMPERATURE STM/S

Yukio HasegawaDr./Associate Professor/The Institute for Solid State Physics, The University of Tokyo. Kashiwa, Japan

Wednesday, March 19, 2008, 1:30PM, Rm. H107, Bldg. 217.

By using scanning tunneling microscopy (STM), we can make images of various physical properties in nanometer-scale spatial resolutions. Here, I demonstrate imaging of electrostatic potential and superconductivity by STM. The electrostatic potential around a charge is described with the Coulomb potential. If the charge is located in a metal, the potential is modified because of the electrons in the host. The potential modification, called screening, is one of the fundamental phenomena in the condensed matter physics. Using low-temperature STM we have developed a method to measure electrostatic potential in high spatial and energy resolutions, and observed the potential around external charges screened by two-dimensional surface electronic states. Characteristic potential decay and the Friedel oscillation were clearly observed around the charges. Superconductivity of nano-size materials, whose dimensions are comparable with the coherent length, is quite different from their bulk. We investigated superconductivity of ultra thin Pb islands by directly measuring the superconducting gaps using STM. The obtained tunneling spectra exhibit a variation of zero bias conductance (ZBC) with a magnetic field, and spatial mappings of ZBC revealed the vortex formation. Details of the imagings will be discussed at the presentation.

The ongoing miniaturization of magnetic devices towards the limit of single atoms calls for appropriate tools to study their magnetic properties. We demonstrate the ability to detect magnetization curves of individual magnetic atoms adsorbed on a metallic substrate using a scanning tunneling microscope with a spin-polarized tip. This enables to map tiny magnetic interactions on the atomic length scale which is evidenced by measuring the RKKY-like indirect exchange between a cobalt adatom and a cobalt nanowire on platinum(111). The method allows for future application to magnetic defects in semiconductors, in order to improve our understanding of diluted magnetic semiconductors. As a first step we will show our detailed investigation of the electronic structure of Mn acceptors in InAs.

THE ESTIMATION OF SPIN-PENETRATION DEPTH IN FERROMAGNETIC METALS

Satoshi YakataDr. - Tohoku University. Sendai,

Thursday, March 6, 2008, 9:15AM, Rm. H107, 217 Bldg.

In the development of spintronics device like a MRAM, the spin-current-induced magnetic reversal is important, because it is expected to reduce the power consumption of device. The penetration depth of transverse component of spin-current is the distance the induced spin relax in ferromagnetic metals and it influence the behavior of spin-current-induced magnetic reversal. In this work, we report the experimental determination of the spin-penetration depth.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

CNST ELECTRON PHYSICS GROUP SEMINAR

DIRAC MATERIALS

Recently a new single layer material -- graphene has been discovered. This is a material where Dirac points in the fermionic spectrum lead to a very unusual properties, such as transport properties and impurity states. I will argue that these properties are not unique to graphene and in fact are a direct consequence of Dirac spectrum in fermionic excitation sector. Strong similarities with d-wave superconductors, superfluid 3He, p-wave superconductors and with other materials exhibiting Dirac electronic spectrum are suggestive and offer a unifying perspective. I will argue that this discovery signifies the emergence of a new class of materials, that can be called **Dirac Materials**, the class where nontirivial properties emerge as a direct consequence of Dirac spectrum of excitations. I will address the local electronic properties of graphene such as impurity states, electronic inhomogeneity and discuss broad similarities with dirac physice seen in other materials.

Templated block copolymer lithography is a powerful method of fabricating nanostructures which draws on the combined strengths of both top-down and bottom-up methods. This talk will discuss the fabrication and magnetic properties of ordered and disordered perpendicular CoCrPt magnetic islands in a range of sizes (5-15nm thick, 20-30nm diameter) fabricated by this method. Disordered patterns were obtained by annealing a thin spin-coated film of polystyrene-polyferrocenyldimethylsilane (PS-PFS) block copolymer. Ordered arrays were fabricated by a similar method, except the polymer was first templated using a removable topographic template. While topographical templates have previously been used to impose long-range order on block copolymer systems, their use results in residual surface relief on the substrate and therefore in the finished device, which is generally undesirable. To avoid this, a removable template may be used. The pattern can then be transferred into functional materials such as silica, W or magnetic films to make long-range-ordered dot arrays over planar substrates. In particular, magnetic islands fabricated by this method maintain their perpendicular magnetic anisotropy but show increased coercivity (800-1650 Oe) as compared to the unpatterned film (150 Oe). Since the islands are uniaxial and non-interacting (calculated nearest neighbor fields are 50 Oe, Hc), time-scale-dependent magnetic properties could be characterized using Sharrock's approach. The measurements show switching volumes (V*) on the order of the physical volume of the dots (~5000 nm3) suggesting that the dots switch their magnetization coherently and independently of each other. The advantages of this technique will be discussed for large-area self-assembled nanoscale pattern formation, and how it can be applied to the fabrication of various structures including patterned magnetic media, DNA sorting and detection devices or plasmon waveguides.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

CNST NANOFABRICATION RESEARCH GROUP SEMINAR

NONLINEAR OPTICS IN SILICON PHOTONIC WIRES: THEORY AND APPLICATION

Xiaogang ChenResearch Associate - Columbia University. New York, NY

Wednesday, February 20, 2008, 1:30PM, Rm. H107, 217 Bldg.

Silicon photonic wires (SPW) are deeply scaled silicon waveguides with transverse dimensions much less than 1 ?m. Integrated silicon photonic devices based on SPW generally have very small footprint and very strong light confinement, which lead to many advantageous physical properties: capability for dispersion engineering, high optical-field density, enhanced effective nonlinearity, and intrinsically short carrier lifetime. First, I will present a comprehensive theoretical model developed to describe pulse dynamics in high-index-contrast and anisotropic waveguides. Third-order nonlinearities, dispersion effects up to the third-order and carrier effects are the three major contributors to the rich pulse dynamics in SPW. In this thesis, various nonlinear optical processes in SPW such as stimulated Raman Scattering (SRS), self-phase modulation (SPM), cross-phase modulation (XPM), modulation instability (MI), and third-order dispersion (TOD) induced soliton-radiation effect are studied theoretically and experimentally. In linear regime, I systematically investigated the "dispersion engineering" in SPW and experimentally demonstrated that SPW could support wavelength-division multiplexing (WDM) transmission at 300 Gb/s for intra-chip optical network. SPM of optical pulses with temporal widths in both picosecond and femtosecond regimes is studied experimentally and theoretically. In the femtosecond regime, the interplay of nonlinear effects, group-velocity-dispersion (GVD) and TOD results in soliton-like pulse propagation in SPW. TOD-induced soliton radiation was demonstrated both numerically and experimentally. XPM is studied using two femtosecond pulses. I investigated the time-resolved phase modulation as a manifestation of the walk-off between these two pulses. XPM is also utilized to optically compress a weak 200-fs pulse propagating in the anomalous GVD regime. MI is a four-wave-mixing (FWM) process that is phase-matched by SPM. We demonstrated that strong MI can be observed in silicon photonic wires with lengths of only a few millimeters using numerical simulation. Our results suggest that MI can be employed to design on-chip optical sources with a highly tunable repetition rate. SRS-based optical amplification in silicon waveguide is a significant functionality. I use the model developed in this thesis to study numerically SRS-mediated pulse dynamics, such as Stokes pulse generation from noise and Raman amplification of Stokes pulse.

DC AREA FIB/SEM USERS GROUP MEETING

Rhonda StroudNRL.

David MacMahonMicron.

Brian SchusterARL.

Henri LezecNIST

David ElbertJohns Hopkins University.

Thursday, February 7, 2008, 1:30PM, Room C103/106, Bldg. 215.

A kickoff meeting of the DC-area FIB and FIB-SEM user group will be held at NIST. This first meeting will be a chance for the local FIB users to meet each other, learn about each other's facilities and applications as well as decide on some organizational details. Please join us if you are interested in FIB related topics. The Nanofab Users Information meetings provide an opportunity for users to present work and comments to the Nanofab staff. If you have an idea about a topic you would like to hear more about or if you are interested in presenting to the group please contact. Alexander Liddle, at: alex.liddle@nist.gov Ext. 6050 Sponsors: NIST CNST NanoFab User Group FEI Company

Lei Chen

CNST Nanofab Process Engineer.

Thursday, January 24, 2008, 1:30AM, Rm. H107, Bldg 217.

Plasma deep Si etching has been widely used to produce high aspect-ratio features of Si in the fabrication of microelectromechanical and other micro-structures. In this meeting, we will introduce the "Bosch" deep Si etcher used in the Nanofab and our process development around it. The "Bosch" process consists of sequential, alternating etching and deposition steps using SF6 and C4F8 plasmas. In this talk, our baseline work on the process stability control, the dependence of the etching results on the sample structures (etch area, feature size and mask material) and our new process development on the reduction of sidewall ripples to etch nano-scale structures will be introduced. The Nanofab Users Information meetings provide an opportunity for users to present work and comments to the Nanofab staff. If you have an idea about a topic you would like to hear more about or if you are interested in presenting to the group please contact. Alexander Liddle, at: alex.liddle@nist.gov Ext. 6050

HOMODYNE DETECTION OF DOMAIN WALL OSCILLATIONS

Daniel BedauDipl.-Phys, Scientist - University of Konstanz.

Tuesday, January 22, 2008, 10:30AM, Rm. H107, Bldg. 217.

Laterally confined magnetic domain walls behave like quasiparticles moving in an external potential well created by a geometrical constriction or a pinning defect. Spin torque effects allow to displace the domain wall quasiparticle electrically, by injecting an ac current the domain wall can be excited to resonate inside the potential well.As the domain wall oscillates, the resistance of the magnetic structure is modulated due to the anisotropic magnetoresistance in phase with the domain wall position. If the quasiparticle happens to be excited at the resonance frequency, the varying resistance will rectify the injected high frequency current and a DC voltage is developed across the structure. Using this technique we determined the resonance frequency of the domain wall. At resonance we observed a reduction of the depinning field of the domain wall for currents as low as $2\times10^{10}$ A/m$^2$, allowing us to determine the resonance frequency by a second independent method. The domain wall resonance frequency was measured for different external magnetic fields and was found to be proportional to the external field. By measuring the mean value of the resistance during excitation we identified the oscillation of the domain wall to be confined close to the potential minimum without any large-scale displacement.

For further information contact John Unguris, 301-975-3712, john.unguris@nist.gov

Nanofab User Information Meeting

NANOFAB USERS INFORMATION MEETING- NEW TOOLS IN NANOFAB CLEAN ROOM

J. Alexander LiddleNanofab Manager.

Thursday, January 10, 2008, 1:30PM, Rm. H107, 217 Bldg.

A brief description of the new capabilities added to the clean room will be given. New tools available (parylene deposition, AFM, tabletop SEM), new tools available in the near term (stress measurement, sputterer, wafer bonder) and medium term (mask writer, acid etch bench, atomic layer deposition system, III-V etcher, deep SiO2 etcher)